Through realization of high-speed transmission of networks and improvement of processing capability of processors, it is required in theses days to process a larger amount of data at a higher speed. Therefore, attention is focused on high-speed serial transmission as an input/output interface that can provide a higher transmission rate.
In order to shorten rising and falling times of a signal, a low voltage differential signaling (LVDS) technique is employed, in which an input/output signal has a small amplitude. However, a noise margin reduces if the amplitude is simply made smaller. The signal is transmitted as a differential signal to eliminate a problem due to the reduction of the noise margin.
The improvement of operation speed of the input/output interface is further strongly demanded, and the amplitude in the differential signal is made smaller and smaller. Meanwhile, due to manufacture variations in impurity concentration and in size accompanied by miniaturization of an LSI, variations have become significant in differential amplifier circuit for amplifying the differential signal. That is, variation in an offset voltage of the differential amplifier circuit has become significant. Such a variation in the offset voltage affects large influence to the differential signal of a small amplitude, to deteriorate transmission quality. Therefore, it is strongly demanded to cancel the variation in the offset voltage to suppress the deterioration of the transmission quality.
However, in an offset canceling control method in related arts, a current value flowing through a differential amplifier circuit and an output signal voltage of the differential amplifier circuit are measured and taken into an offset control circuit. The offset control circuit generates an offset cancellation signal based on the measured result and outputs it to the differential amplifier circuit to cancel the offset. However, the current value and the output signal voltage in the differential amplifier circuit change depending on environmental factors such as noise and ambient temperature. Thus, the control thereof is difficult, so that it is difficult to resolve the above problem of the offset voltage.
In addition to the above description, as for a differential amplifier circuit, Japanese Patent Application Publications (JP-P2001-101872A, JP-P2003-045190A, JP-P2003-259564A, JP-P2005-150789A and JP-A-Heisei 8-223228) are known.